In the discussion of the background that follows, reference is made to certain structures and/or methods. However, the following references should not be construed as an admission that these structures and/or methods constitute prior art. Applicant expressly reserves the right to demonstrate that such structures and/or methods do not qualify as prior art.
Currently available cutters include a PCD layer or table supported by or joined coherently to a substrate, post or stud that is generally made of tungsten carbide. Tungsten carbide is generally selected for the substrate because of its excellent mechanical properties like abrasion resistance and compressive strength.
Bonding the diamond layer to the substrate generally occurs during the sintering stage of the diamond layer at high-pressure high-temperature (HPHT). The sintered PCD layer is composed of diamond particles with extensive amounts of direct diamond-to-diamond bonding or contact as the major phase. In the interstices of the diamond particles, for example, the triple grain pockets or grain boundaries, there is a binder phase which is also called the metal phase or the catalyst solvent phase. This secondary phase also forms a network intermingled with the diamond network. The binder phase serves as the catalyst or solution to the growth of the diamond-to-diamond bonding. The binder phase generally includes at least one active metal, for example, but not limited to, cobalt (Co), nickel (Ni), and iron (Fe).
Additional minor phases generally form either in the binder phase or between the binder phase and the diamond particles. These phases may include the metal carbides formed during the sintering process. These phases can form isolated islands and embed in the binder phase without clear boundaries, which can increase crack propagation within the diamond table.
A process generally used for sintering the currently available cutting elements is the HPHT process, an example of which is shown in FIGS. 11 and 12. Specifically, the process includes adding diamond particles 112 and optional sintering aids 114 to a metal container 110. Then, a carbide stud 118, generally tungsten carbide (WC), is inserted into the metal container 110 in contact with the diamond feed 116 including optional sintering aids. The assembly 120 including the container 110, diamond feed 116 and carbide stud 118 is subjected to the HPHT process. During the HPHT process, the binder originally present in the carbide stud will be molten and squeezed into the diamond compact due to the high temperature 124 and pressure 122. The flow of the binder phase is also called sweep due to the fact that molten binder (arrows 126 representing direction of molten binder) will form a front face 128 while infiltrating, which carries binder and other materials from the stud to the diamond feed.
When the diamond is submerged or surrounded by the sweeping binder phase, the diamond sintering takes place via the liquid-sintering mechanism of solution-transportation-reprecipitation. Here the diamond-to-diamond bonding is formed and the network of diamond is built. Thus, after sintering, a compact 100 is formed having a diamond layer 102 and a carbide stud 104 bonded together at an interface.
The binder from the stud also carries certain amounts of dissolved species from the stud into the diamond layer. The amount of the species depends strongly upon the pressure and temperature. Species that are carried with the binder include, for example, tungsten and carbon. The dissolved tungsten will react with solvent metal and/or carbon from the diamond feed and carbide stud. Depending on the pressure, temperature, and the composition, the reaction products might stay in the binder phase as solid solution species or precipitate out as carbide-based phases after cooling down to room temperature when the process is finished. This binder phase and other precipitated minor phases remain in the sintered diamond layer in between the grains and form a network.
Further, in drilling applications, PCD cutters are subjected to high impact loads which may lead to chipping and spalling of the cutters. The spalls originate from microcracks generated at high stress points. If these cracks reach a tougher phase within the PCD, they may be deflected or arrested, thus improving the impact toughness of the PCD. Several methods have been proposed to provide this improved impact toughness. For example, U.S. Pat. No. 6,974,624 demonstrates a PCD-WC composite cutter wherein PCD is enclosed in honeycomb-like WC shells. Further, European Patent Number 0 699 642 discloses that PCD is reinforced with fibers to improve impact toughness. If the fibers survive the sintering process, they act as a tough phase within PCD and arrest or deflect cracks within the PCD. However, none of the prior art solves all of the disadvantages of a traditional diamond layer for a cutter formed during a sintering process.